1. Field of the Invention
The present invention relates to a subminiature imaging optical system, and more particularly, to a subminiature imaging optical system installed in a mobile communication terminal and a personal digital assistant (PDA) or utilized in a surveillance camera and a digital camera.
2. Description of the Related Art
In general, mobile communication terminals had only functions of basic communication at their incipient stage. However, with increased use, the mobile communication terminals are required to have diversified functions ranging from photographing to image transmission and video communication, continuously evolving in their functions and services. Recently, a new expanded concept of mobile communication terminal by integrating digital camera technology with mobile phone technology, i.e., so called camera phones or camera mobile phones are significantly attracting attention.
In particular, the imaging optical system mounted on the camera phone is not only required to be miniaturized, light-weight and low-cost, but also have high resolution since the pixel size of an image sensor formed of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) used in the imaging optical system is decreasing.
In order to satisfy miniaturization and low cost, the imaging optical system mounted on a small device such as a mobile phone needs to have lenses of as small a number as possible, but this restricts a degree of freedom in designing and undermines the optical capabilities.
Meanwhile, the imaging optical system may employ lenses formed of glass and plastic, respectively to achieve better optical capabilities and aberrational corrections. This construction may satisfy high pixel requirements, but degrades color definition due to increase in chromatic aberration. Besides, this renders the imaging optical system hardly miniaturizable enough to suit consumer's needs.
In addition, the conventional imaging optical system formed of lenses having positive, negative and positive refractive powers allows chromatic aberration and other aberrations to be corrected relatively easily but requires highly precise machining owing to the lenses formed of all aspherical surfaces.